A kind of generation device of continuous variable many components polarization-entangled light field
Technical field
The present invention relates to the generation device of non-classical optical state, specifically a kind of generation device of continuous variable many components polarization-entangled light field.
Background technology
Quantum entanglement is the important content in quantum mechanics, be also realize quantum information, quantum calculation and quantum metering valuable source.Continuous variable quantum entanglement is due to its decisive preparation and measure the extensive concern that the high advantage of efficiency causes researchist.Along with the development of quantum information, quantum network becomes current study hotspot, and this tangles light field to many components and proposes requirement.Light due to velocity of propagation fast, and weak with the interaction of surrounding environment, be the ideal carrier that quantum information is propagated.Atom due to its have good coherence, can be handling, can as the network node of quantum information storage and process.The polarized component of light field is corresponding with the automatic rotary component of atom, all describes by Stokes vector, can direct interaction, and measures and do not need local oscillations light field, and system architecture is compact.Therefore, continuous variable many components polarization-entangled light field is the key of quantum network development.It can act on mutually with the multiple nodes in quantum network, and then realizes quantum storage.In addition, the polarization state of light field also can be mapped to the spin state of atom by it, makes to set up Entanglement between the different nodes in quantum network, and then in quantum network, transmits arbitrarily quantum state, realize quantum internet.
At present, optical parametric amplifier is a kind of effective means of preparation continuous variable non-classical optical state.In 2002, the people such as Ping KoyLam have delivered the paper of " Experimental Demonstration ofContinuous Variable Polarization Entanglement " on PHYSICAL REVIEW LETTERS, and first this paper utilizes two by LiNbO
3the optical parametric amplifier that crystal is formed obtains quadrature squeezing light field, then utilizes the interference system of an optical beam splitting sheet and two polarization beam splitter prism compositions to obtain continuous variable two component polarization-entangled light field.
In above-mentioned article, they obtain continuous variable two component polarization-entangled light field.But the wavelength of the light field of above-mentioned article is 1064nm, do not have corresponding Atomic absorption line, practical quantum network requires that the Absorption Line of the materials such as the wavelength of many components polarization-entangled light field and atom matches.Secondly, above-mentioned article is the polarization-entangled between two-beam field, and quantum network proposes requirement to the polarization-entangled between multi beam light field.
Summary of the invention
The object of this invention is to provide a kind of frequency-tunable, the multi beam continuous variable polarization-entangled light field that the space that wavelength is corresponding with Atomic absorption line is separated.Light field polarized component and atomic spin component can direct interactions, and its measuring system does not need local oscillated signal, may be used for quantum network.
The generation device of a kind of continuous variable many components polarization-entangled light field of the present invention's design, comprises ti sapphire laser, secondary harmonic generator, multiple optical parametric amplifier, interference system and many cover Stokes measuring systems.It is λ that described ti sapphire laser produces wavelength
0the light field a of (this wavelength is corresponding with rubidium Atomic absorption line)
0, a part of laser is as the signal light field of multiple optical parametric amplifier; It is λ that another part laser injection secondary harmonic generator obtains wavelength
p=λ
0the light field a of/2
p, as the pumping light field of multiple optical parametric amplifier; It is λ that multiple optical parametric amplifier produces multi beam wavelength respectively
0orthogonal amplitude or orthogonal phase squeezing light field a
1, a
2..., a
n; Interference system comprises optical beam splitting sheet interference system and polarization beam splitter prism interference system, is obtained that the many components of continuous variable are orthogonal tangles light field by optical beam splitting sheet interference system, then is converted to continuous variable many components polarization-entangled light field by polarization beam splitter prism; Utilize the polarized component of Stokes measuring system to light field to measure, and verify Entanglement;
Described optical parametric amplifier, comprises optical resonator and nonlinear crystal, and the transmitance of the output coupling mirror of described optical resonator is 5-6%, and described nonlinear crystal is PPKTP crystal;
Described optical beam splitting sheet interference system by multiple optical beam splitting sheet (as during three components 2, four components time 3 optical beam splitting sheets) form, the relative phasic difference of interference optical field accurately controls and is locked in 0 or Pi/2;
Described polarization beam splitter prism interference system is made up of multiple polarization beam splitter prism, and as the polarization beam splitter prism composition of 3,4,6,8 or more, the relative phasic difference of interference optical field accurately controls and is locked in 0 or Pi/2.
Described ti sapphire laser, has high-output power, low-noise characteristic, may be used for the preparation of tangling light field, and has frequency-tunable characteristic, can be locked in Atomic absorption line.
Described optical resonator adopts the standing-wave cavity structure be made up of two panels concave mirror, or adopts the borders ring cavity structure be made up of two panels concave mirror and the flat mirror of two panels.
The crystal that described optical parametric amplifier adopts is PPKTP nonlinear crystal.Optical parameter process can adopt traditional phase-matching crystals in the prior art.The device of seminar of Australia employs LiNbO
3crystal, achieves the nonlinear interaction of the light field of wavelength 1064nm.Lbo crystal is usually used in the nonlinear interaction of the light field of wavelength (795nm) corresponding with rubidium atom D1 Absorption Line.This crystal thermal effect is not obvious, can use under high power conditions, has achieved the second_harmonic generation that efficiency reaches the chamber enhancing of 80%.But its effective nonlinear coefficient is not high, be 0.75pm/V, secondly owing to there is serious walk-off effect, the beam quality obtained is bad, and needs to operate under the high temperature conditions.The cyclic polarization technique that developed recently gets up, by the mechanical periodicity of nonlinear optical coefficients, realizes quasi-phase matched, as PPLN crystal and PPKTP crystal etc.This technology can utilize the maximum nonlinear factor of crystal, the effective nonlinear coefficient of PPLN crystal reaches 17 to 18pm/V, the effective nonlinear coefficient of PPKTP crystal is 7 to 9pm/V, and all realize nonlinear interaction by this technology at any wavelength of the transparent wave band of crystal, and effectively can solve walk-off effect, the beam quality obtained.Intensity of compression is very responsive to the loss of optical parametric amplifier, very high to the requirement of loss.PPKTP crystal is compared with PPLN crystal, and advantage is the preparation that less loss is suitable for non-classical optical state, and operates at ambient temperature.Although PPKTP crystal exists thermal effect, crystal is applicable to the situation of low pump power, and thermal effect is also not obvious.In sum, the optical parametric amplifier of PPKTP crystal is utilized under low pump power, normal temperature, steady running can to obtain the light field of higher compression degree, the better beam quality that wavelength is 795nm.
The transmitance of the output coupling mirror of described optical parametric amplifier is 5-6%, if this transmitance is excessive, the threshold power of system is by too high, if this transmitance is too small, the intensity of compression of the light field that system produces will be less.Therefore, suitable output coupling mirror transmitance can make optical parametric amplifier steady running under low pump power condition, obtains the light field of higher compression degree.
Described Stokes measuring system is by λ/2 wave plate, and λ/4 wave plate, polarization beam splitter prism and power add, subtracter composition.Utilize Stokes measuring system can realize measuring 4 polarized components of light field, namely utilize polarization beam splitter prism and power adder to stokes component S
0measure, utilize polarization beam splitter prism and power subtracter to stokes component S
1measure, utilize polarization beam splitter prism, λ/2 wave plate and power subtracter to stokes component S
2measure, utilize polarization beam splitter prism, λ/4 wave plate and power subtracter to stokes component S
3measure.
The generation device of continuous variable many components polarization-entangled light field of the present invention's design has following advantage compared with the same device reported:
1 low noise, tunable ti sapphire laser and the optical parametric amplifier be made up of PPKTP crystal may be used for the optical nonlinearity effect that wavelength is the light field of 795nm.Wavelength and the rubidium atom D1 Absorption Line of the polarization-entangled light field that this device obtains match, and can be applied to quantum and store, and the interaction of light field and atom.
2 optical parametric amplifiers use high effective nonlinear coefficient and low-loss, PPKTP crystal without walk-off effect, with the output coupling mirror of suitable transmitance, under low pump power, normal temperature, steady running the light field of higher compression degree, better beam quality can be obtained.
The light field that more than 3 optical parametric amplifier and interference system produce has the continuous variable polarization-entangled characteristic between the multi beam light field of space separation, can be applied to quantum network.
In a word, the present invention has prepared frequency-tunable, the multi beam continuous variable polarization-entangled light field that the space that wavelength is corresponding with Atomic absorption line is separated, light field polarized component and atomic spin component can direct interactions, its measuring system does not need local oscillated signal, can realize quantum and store and quantum network.
Accompanying drawing explanation
The generation device structural representation of Fig. 1 continuous variable three of the present invention component GHZ class polarization-entangled light field.
Fig. 2 the present invention is used for the interference system structural representation of continuous variable three component GHZ class polarization-entangled light field.
The generation device experimental result picture of Fig. 3 continuous variable three of the present invention component GHZ class polarization-entangled light field.
The generation device structural representation of Fig. 4 continuous variable four of the present invention component GHZ class (Cluster class) polarization-entangled light field.
Fig. 5 the present invention is used for the interference system structural representation of continuous variable four component GHZ class (Cluster class) polarization-entangled light field.
Embodiment
Below in conjunction with accompanying drawing, the present invention is further described:
The generation device of embodiment 1. continuous variable three component GHZ class polarization-entangled light field.
The generation device of a kind of continuous variable three component GHZ class polarization-entangled light field as shown in Figure 1, comprises ti sapphire laser 1, secondary harmonic generator 2, three optical parametric amplifiers 31,32,33, interference system 4 and three cover Stokes measuring systems 5.
Described interference system 4, as shown in Figure 2, comprises the interference system that a slice 1:1 optical beam splitting sheet (BS), a slice 1:2 optical beam splitting sheet (BS) and three polarization beam splitter prisms (PBS) are formed, orthogonal amplitude squeezed light field a
2with orthogonal position phase light field a
3interfered by 1:2 optical beam splitting sheet, and the relative phasic difference controlling them is 0, a branch of of interference optical field passes through 1:1 optical beam splitting sheet and orthogonal amplitude squeezed light field a again
1interfere, and the relative phasic difference controlling them is 0, can obtain that three component GHZ classes are orthogonal tangles light field, then interfered by the coherent states field of three polarization beam splitter prisms and more than 30 times power, and the relative phasic difference controlling them is Pi/2, be converted to continuous variable three component GHZ class polarization-entangled light field a
x, a
yand a
z.
Low noise, tunable ti sapphire laser 1 produce the light field a that wavelength is 795nm
0, be divided into two parts, a part of laser is as the signal light field of three optical parametric amplifiers 31,32,33, and another part laser injects secondary harmonic generator 2 and obtains the light field a that wavelength is 398nm
p, as the pumping light field of three optical parametric amplifiers, three optical parametric amplifiers are formed by optical resonator and nonlinear crystal, optical resonator adopts the standing-wave cavity structure be made up of two panels concave mirror, the transmitance of output coupling mirror is 5.6%, nonlinear crystal is PPKTP crystal, under three optical parametric amplifiers are operated in the condition of normal temperature and low pump power, steady running obtains higher compression degree, the compressed state optical field of better beam quality, wherein, first optical parametric amplifier 31, second optical parametric amplifier 32 produces the orthogonal amplitude squeezed light field a that two bundle wavelength are 795nm respectively
1, a
2, the 3rd optical parametric amplifier 33 produces the orthogonal phase squeezing light field a that a branch of wavelength is 795nm
3, obtained by optical beam splitting sheet interference system as shown in Figure 2 that continuous variable three component is orthogonal tangles light field, then be converted to continuous variable three component GHZ class polarization-entangled light field a by polarization beam splitter prism interference system as shown in Figure 2
x, a
yand a
z, finally utilize polarization beam splitter prism, λ/2 wave plate and power subtracter to stokes component S
2measure, utilize polarization beam splitter prism, λ/4 wave plate and power subtracter to stokes component S
3measure, and verify Entanglement.
If the quadrature component of light field meets following two inequality as follows:
<δ
2(S
3x-S
3y)>+<δ
2(S
2x+S
2y+S
2z)>≤4
<δ
2(S
3x-S
3z)>+<δ
2(S
2x+S
2y+S
2z)>≤4
So, this light field is just referred to as three component GHZ class polarization-entangled light fields.Wherein, S
2and S
3represent the stokes component in 45 degree of directions and right-hand circular polarization direction respectively.These examples of implementation can obtain the continuous variable three component GHZ class polarization-entangled light field that wavelength is 795nm under normal temperature condition.
Usual experimental result is normalized, and uses I
1(S
3, S
2), I
2(S
3, S
2) represent and the correlated noise of continuous variable polarized component correspond respectively to above-mentioned two inequality, wherein:
The generation device experimental result of continuous variable three component GHZ class polarization-entangled light field as shown in Figure 3.In figure, curve I represents quantum noise limit, and curve II represents the correlated noise measuring the three component polarized components obtained.In figure, ordinate corresponds to above-mentioned normalized polarized component correlated noise I
1(S
3, S
2), I
2(S
3, S
2), horizontal ordinate corresponds to analysis frequency, and unit is megahertz.This correlated noise is less than the existence that 1 shows quantum entanglement, namely obtains continuous variable three component GHZ class polarization-entangled light field.
The generation device of embodiment 2. continuous variable four component GHZ class or Cluster class polarization-entangled light field.
The generation device of a kind of continuous variable four component GHZ class polarization-entangled light field as shown in Figure 4, comprises ti sapphire laser 1, secondary harmonic generator 2, four optical parametric amplifiers, interference system 4 and four cover Stokes measuring systems 5.
Described interference system 4, as shown in Figure 5, comprises the interference system that three 1:1 optical beam splitting sheets (BS) and four polarization beam splitter prisms (PBS) are formed, orthogonal amplitude squeezed light field a
2and a
3interfered by 1:1 optical beam splitting sheet, and the relative phasic difference controlling them is Pi/2, a branch of of interference optical field passes through 1:1 optical beam splitting sheet and orthogonal phase squeezing light field a again
1interfere, and the relative phasic difference controlling them is 0, another bundle of interference optical field is again by 1:1 optical beam splitting sheet and orthogonal phase squeezing light field a
4interfere, and the relative phasic difference controlling them is 0 (or Pi/2), can obtain that four component GHZ classes (Cluster class) are orthogonal tangles light field, different association types can be obtained by the intervention phase difference of control both optical beam splitter, then interfered by the coherent states field of four polarization beam splitter prisms and more than 30 times power, and controlling relative phasic difference is Pi/2, be converted to continuous variable four component GHZ class (Cluster class) polarization-entangled light field a
x, a
y, a
zand a
w.
Low noise, tunable ti sapphire laser 1 produce the light field a that wavelength is 795nm
0, be divided into two parts, a part of laser is as the signal light field of four optical parametric amplifiers 31,32,33,34, and another part laser injects secondary harmonic generator 2 and obtains the light field a that wavelength is 398nm
p, as the pumping light field of four optical parametric amplifiers, four optical parametric amplifiers are formed by optical resonator and nonlinear crystal, optical resonator adopts the standing-wave cavity structure be made up of two panels concave mirror, the transmitance of output coupling mirror is 5.6%, nonlinear crystal is PPKTP crystal, under four optical parametric amplifiers are operated in the condition of normal temperature and low pump power, steady running obtains higher compression degree, the compressed state optical field of better beam quality, wherein, second optical parametric amplifier 32, 3rd optical parametric amplifier 33 produces the orthogonal amplitude squeezed light field a that two bundle wavelength are 795nm respectively
2, a
3, the first optical parametric amplifier 31, the 4th optical parametric amplifier 34 produce the orthogonal phase squeezing light field a that two bundle wavelength are 795nm respectively
1, a
4, obtained by optical beam splitting sheet interference system as shown in Figure 5 that continuous variable four component is orthogonal tangles light field, then be converted to continuous variable four component GHZ class or Cluster class polarization-entangled light field a by polarization beam splitter prism interference system as shown in Figure 5
x, a
y, a
zand a
w, finally utilize polarization beam splitter prism, λ/2 wave plate and power subtracter to stokes component S
2measure, utilize polarization beam splitter prism, λ/4 wave plate and power subtracter to stokes component S
3measure, and verify Entanglement.
If the quadrature component of light field meets following three inequality as follows:
<δ
2(S
2x-S
2y)>+<δ
2(S
3x+S
3y+S
3z+S
3w)>≤1
<δ
2(S
2y-S
2z)>+<δ
2(S
3x+S
3y+S
3z+S
3w)>≤1
<δ
2(S
2z-S
2w)>+<δ
2(S
3x+S
3y+S
3z+S
3w)>≤1
So, this light field is just referred to as four component GHZ class polarization-entangled light fields.
If the quadrature component of light field meets following three inequality as follows:
<δ
2(S
3x+S
3y+S
3z)>+<δ
2(S
2x-S
2y)>≤1
<δ
2(S
3z-S
3w)>+<δ
2(-S
2y+S
2z+S
2w)>≤1
<δ
2(S
3x+S
3y+2S
3z)>+<δ
2(-2S
2y+S
2z+S
2w)>≤2
So, this light field is just referred to as four component C luster class polarization-entangled light fields.These examples of implementation can obtain continuous variable four component GHZ class that wavelength is 795nm or Cluster class polarization-entangled light field under normal temperature condition.
Core of the present invention is a kind of device producing continuous variable many components polarization-entangled light field.This invention utilizes optical parametric amplifier to produce quadrature squeezing light field, then obtains continuous variable many components polarization-entangled light field by interference system.It is corresponding with Atomic absorption line that this device can stablize a kind of wavelength of generation under normal temperature condition, many components continuous variable polarization-entangled light field that space is separated, be convenient to directly and atomic spin interaction, measuring system do not need the advantages such as local oscillated signal, and can quantum network be applied to.